how to get materials to transfer to billing on existing job card?

materials selected by a customer in a "service" (self serve) automatically transfer to billing section of job card if you convert the "service" when it arrives as an inbox enquiry. When you receive the service as an inbox enquiry and opt to "attach to existing job" (not convert to new), the materials are not transferring to the billing section of the existing job card- how do i connect this?